Selective depletion of organic matter in mottled podzol horizons

Some well-drained podzols on quartz sands in the Netherlands and neighbouring Belgium and Germany show mottling in all horizons due to selective removal of organic matter. Phospholipid analysis and morphology of the mottles suggests that this removal is due to a combination of bacteria, fungi, and actinomycetes. Investigation by pyrolysis-GC/MS of organic matter in the depleted zones as compared to their surroundings indicates (1) selective decay of relatively palatable components, (2) residual accumulation of aliphatic biopolymers such as cutan and suberan that produce alkanes, alkenes and methylketones upon pyrolysis, and (3) accumulation of microbial polysaccharides and N-containing compounds. Although the selective organic matter decay in the depleted mottles is similar to the process that causes degradation of organic matter at the top of the B-horizon and its conversion to an E-horizon, the essential difference is that, while decay at the E–B-horizon transition in podzols is governed by the presence or absence of aluminium and iron, the micro flora that is responsible for the decay mottles acts independently from metal concentrations.